1. Field of the Invention
This invention relates generally to the detection of impurities in fluids, and more particularly to the detection of corrosive impurities in the core cooling water of nuclear fission light water reactors (LWR).
2. Description of the Prior Art
Stress enhanced intergranular attack has been observed to occur in metal used in LWRs under certain conditions of composition, temperature, stress and configuration. Materials such as 304 stainless steel and Inconel 600 have been observed to be susceptible to cracking and pitting due to this mechanism. Other alloys, especially low carbon stainless steels, are much less susceptible under normal operating circumstances of LWRs. Unfortunately, reactor internals and piping in many LWRs now use materials that suffer from potential intergranular attack.
Materials cracks are also affected measurably by cooling water impurities. LWRs have systems to monitor water purity and maintain the water at acceptable impurity levels under normal operating conditions. However, impurity intrusions occur occasionally, impacting water quality which may or may not have an effect on the LWR system materials. Presently, there are no means for quantitatively measuring the impact of the intrusion events prior to the damaging of the LWR vessel internals, which damage, for example, can occur to the local power range monitors (LPRM) and would become apparent only when the signals emerging from the LPRM's vary erratically or suddenly shift to new relatively constant values.
Sometimes the damage to or failure of LWR vessel internal equipment occurs for reasons other than water impurity. At present it is not possible to determine the cause of such failures in a number of circumstances. This results in reactor shutdown in order to determine if the cause is due to water impurity. The result may be that the reactor shutdown is unnecessary; this is quite costly to the operator of the reactor. Additionally, it would be desirable to know of the presence of impurities in the cooling water well in advance of the impurities causing damage to LWR vessel internals.
Therefore, a need exists for a sensor capable of detecting impurities in LWR cooling water as soon as possible after the impurities are present.